3D printing with PHT/PHA based materials and polymerizable monomers

ABSTRACT

This application describes methods of forming an object. The methods described include forming a mixture with i) one or more primary diamines, ii) one or more polymerizable monomers, iii) a formaldehyde-type reagent, and iv) a polymerization initiator; forming a gel by heating the mixture to a temperature of at least 50° C.; and curing the one or more polymerizable monomers by activating the polymerization initiator. The one or more primary diamines may include one or more amine functional oligomers and/or primary aromatic diamine small molecules. The one or more polymerizable monomers may include styrenics, acrylates, methacrylates, vinyl esters, unsaturated polyesters, and derivatives thereof. The gel is a polyhemiaminal (PHA), a polyhexahydrotriazine (PHT), and/or a polyoctatriazacane (POTA) polymer, and curing of the gel forms an interpenetrating network of the PHA/PHT/POTA and the polymer formed from the polymerizable monomers.

FIELD

The present disclosure relates to new 3D printing methods and apparatus.Specifically, new materials are disclosed for use in 3D printingmethods, with apparatus for performing such methods.

BACKGROUND

3D printing has attracted significant attention for its potential as anew manufacturing process offering remarkable versatility in the abilityto rapidly produce tailored physical objects from the micro to macroscale. While the foundations of this technology were laid in the late1980's, modern advancements have produced 3D-printers for applicationssuch as personal home use, rapid prototyping, and production ofbiomedical devices. Hofmann, M.; ACS MacroLett., 2014, 3, 382-286. Whilethe hardware utilized in this field is rapidly maturing the number ofmaterials used in the printing process generally, rely on traditionalcommercial polymers such as poly(methyl methacrylate), for instance.However, in academic settings more exotic materials are in the phases ofexploratory research. Sun, K., Wei, T. S., Ahn, B. Y., Seo, J. Y.,Dillon, S. J., Lewis, J. A., Adv. Mater., 2013, 25, 4539-4543.

The field of 3D-printing can be significantly impacted by expanding therepertoire of materials available (and associated properties) asprintable media. The ability to rapidly form dynamically crosslinkednetworks during material deposition is an attractive property for aprintable medium. Extensive crosslinking of such a medium would yield arigid structure with mechanical properties that could facilitate theprinting of macroscale objects. In addition, a material with reversiblethermosetting properties would allow one to modify a physical objectafter it is printed, offering an additional level of control notavailable when traditional materials are utilized as print media. Inaddition, the blending of materials that can participate in networkformation would provide tailorable mechanical properties in the finalstructure. Use of such materials in 3D-printing methods and apparatuswould expand the applicability of 3D printing.

SUMMARY

This application describes methods of forming an object. The methodsdescribed include forming a mixture with i) one or more primarydiamines, ii) one or more polymerizable monomers, iii) aformaldehyde-type reagent, and iv) a polymerization initiator; forming agel by heating the mixture to a temperature of at least 50° C.; andcuring the one or more polymerizable monomers by activating thepolymerization initiator. The one or more primary diamines may includeone or more amine functional oligomers, examples of which includepolyethers, polyesters, polystyrenics, polyacrylates, polymethacrylates,polycyclooctene, polyamides, and polynorbornenes, and derivativesthereof. The one or more primary diamines may also include a primaryaromatic diamine. The one or more polymerizable monomers may includestyrenics, acrylates, methacrylates, vinyl esters, unsaturatedpolyesters, and derivatives thereof.

Some methods of forming an object described in this application includeflowing a first mixture comprising a formaldehyde-type reagent through afirst pathway, flowing a second mixture comprising a primary diaminethrough a second pathway, mixing the first and second mixtures to form aPHA, PHT, or POTA precursor, flowing the PHA, PHT, or POTA precursor toa nozzle of a 3D printer, supplying heat to the nozzle of the 3D printerto heat the PHA, PHT, or POTA precursor to a temperature of at least 50°C., dispensing the PHA, PHT, or POTA precursor in a pattern onto asubstrate to form a precursor object comprising a PHA, PHT, or POTAcross-linked polymer, and hardening the PHA, PHT, or POTA precursor intoa polymer by heating the precursor object to a temperature of at least50° C.

The PHA and PHT polymers are formed by reacting a primary diamine with aformaldehyde-type reagent. The POTA polymer is formed by reacting aprimary diamine with a formaldehyde-type reagent and formic acid. Theobjects formed using the methods described herein may be made of asingle polymer, a single polymer type using multiple diamine monomers,or a mixture of PHA, PHT, and/or POTA polymers with different desiredphysical properties.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a schematic side view of a 3D printing apparatus according toone embodiment.

FIG. 2 is a schematic side view of a 3D printing apparatus according toanother embodiment.

FIG. 3A is a cross-sectional view of a nozzle according to oneembodiment that may be used in the 3D printing apparatus of FIGS. 1 and2.

FIG. 3B is a cross-sectional view of a nozzle according to anotherembodiment that may be used in the 3D printing apparatus of FIGS. 1 and2.

FIG. 4A is a process diagram illustrating aspects of processes accordingto one embodiment.

FIG. 4B is a process diagram illustrating other aspects of the processembodiments of FIG. 4A.

FIG. 4C is a process diagram illustrating aspects of processes accordingto another embodiment.

FIG. 4D is a process diagram illustrating other aspects of the processembodiments of FIG. 4C.

DESCRIPTION OF THE EMBODIMENTS

Polyhemiaminals (PHA's), polyhexahydrotriazines (PHT's), andpolyoctatriazacanes (POTA's) are new polymeric materials that may beadvantageously used to form composite materials having advantageousproperties. The composite materials described herein are mixtures of afirst material that includes a PHA, PHT, and/or POTA polymer with asecond material formed from polymerizable monomers. The mixtures may bean interpenetrating network of the first material and the secondmaterial that may be formed by mixing together i) one or more primarydiamines, ii) one or more polymerizable monomers, iii) aformaldehyde-type reagent, and iv) a polymerization initiator, heatingthe mixture to a temperature of at least 50° C. to form a gel, andcuring the polymerizable monomers by activating the polymerizationinitiator. Typically, such a material will have homogeneous compositionand properties. Alternately, a micro-heterogeneous material may beformed by forming the second material, reducing the second material to apowder of a desired morphology, mixing the powder with one or moreprimary diamines and a formaldehyde-type reagent, and heating theresulting mixture to a temperature of at least about 50° C. In such aprocess, a polymer product is formed comprising a PHA, PHT, and/or POTApolymer matrix with dispersed domains of another polymer formed frompolymerizable monomers.

The gel is typically a thixotropic or elastomeric material that may bedeformed, extruded, or dispensed in a convenient way. A gel is a dilutecross-linked system that exhibits no flow in the steady state. Athixotropic material is a material whose viscosity decreases when thematerial is sheared. An elastomeric material is a polymer that isviscoelastic. A viscoelastic material is a material that has bothviscosity, resistance to shear, and elasticity, development of arestorative force when strained. Such materials can be shaped and flowedto an extent such that the material can be dispensed onto a substrate ina two-dimensional or three-dimensional form, and the material will holdits shape and position after being dispensed onto the substrate.

The properties of the gel may be controlled by adjusting the compositionof the reaction mixture. For most applications, below about 200° C. thegel will have a viscosity shear coefficient between about 5 MPa andabout 70 MPa, for example about 35 MPa.

The first material may include a PHA material. A PHA material is acrosslinked polymer comprising i) a plurality of trivalent hemiaminalgroups of formula (1):

covalently linked to ii) a plurality of bridging groups of formula (2):

wherein y′ is 2 or 3, and K′ is a divalent or trivalent radical. Herein,starred bonds represent attachment points to other portions of thechemical structure. Each starred bond of a given hemiaminal group iscovalently linked to a respective one of the bridging groups.Additionally, each starred bond of a given bridging group is covalentlylinked to a respective one of the hemiaminal groups.

As an example, a polyhemiaminal can be represented by formula (3):

In this instance, each K′ is a trivalent radical (y′=3) comprising atleast one 6-carbon aromatic ring. It should be understood that eachnitrogen having two starred wavy bonds in formula (3) is a portion of adifferent hemiaminal group.

Non-limiting exemplary trivalent bridging groups include:

The bridging groups can be used singularly or in combination.

Each K′ can also be a divalent bridging group. PHA's including divalentbridging groups K′ can be represented herein by formula (4):

wherein K′ is a divalent radical (y′=2 in formula (2)) comprising atleast one 6-carbon aromatic ring. Each nitrogen having two starred wavybonds in formula (4) is a portion of a different hemiaminal group.

More specific divalent bridging groups K′ may have the formula (5):

wherein L′ is a divalent linking group selected from the groupconsisting of *—O—*, *—S—*, *—N(R′)—*, *—N(H)—*, *—R″—*, andcombinations thereof, wherein R′ and R″ independently comprise at least1 carbon. In an embodiment, R′ and R″ are independently selected fromthe group consisting of methyl, ethyl, propyl, isopropyl, phenyl, andcombinations thereof. Other L′ groups include methylene (*—CH₂—*),isopropylidenyl (*—C(Me)₂-*), and fluorenylidenyl:

PHA's including divalent bridging groups of formula (5) can berepresented herein by formula (6):

wherein L′ is a divalent linking group selected from the groupconsisting of *—O—*, *—S—*, *—N(R′)—*, *—N(H)—*, *—R″—*, andcombinations thereof, wherein R′ and R″ independently comprise at least1 carbon. Each nitrogen having two starred wavy bonds in formula (6) isa portion of a different hemiaminal group.

The hemiaminal groups can be bound non-covalently to water and/or asolvent. A non-limiting example is a hemiaminal group that is hydrogenbonded to two water molecules as shown in formula (7):

The first material may also include a PHT material. A PHT material is acrosslinked polymer comprising i) a plurality of trivalenthexahydrotriazine groups of formula (8):

covalently linked to ii) a plurality of the bridging groups K′, withstarred bonds being defined as above.

A PHT including bridging groups of formula (5) can be represented byformula (9):

wherein L′ is defined as above. Each nitrogen having two starred wavybonds in formula (9) is a portion of a different hexahydrotriazinegroup.

The first material may also include a POTA material. A POTA material isa polymer with a plurality of trivalent octatriazacane group having thegeneral structure

A plurality of the trivalent octatriazacane groups of formula (10) arebonded, at the starred bonds, to divalent linking groups having thegeneral structure *-J′-*, where J′ comprises an aromatic group. Apolyoctatriazacane according to formula (10) may be made by mixingtogether a diamine, or a mixture of diamines, having the generalstructure H₂N-J′-NH₂, where J′ is defined as above, with an aldehyde(i.e. formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, etc.),a solvent, and formic acid.

J′ may be a substituted or unsubstituted phenylene group having thegeneral structure of formula (11):

where R¹, R², R³, and R⁴ are each, individually, H, Cl, CN, F, NO₂, SO₃,heterocycles such as imides, benzoxazoles, benzimidazoles, andphenylquinoxalines, C_(x)H_(2x+1−y)R⁵ _(y), or C₆H_(5−a)R⁵ _(a), whereR⁵ is Cl, F, SO₃, C₆H_(5−a)R⁶ _(a), or NH_(3−b)R⁶ _(b), where R⁶ isC_(x)H_(2x+1), C_(x)H_(2x), or C₆H₅, where in each instance x is aninteger from 1 to 4, y is an integer from 0 to 2x+1, a is an integerfrom 0 to 5, and b is an integer from 0 to 3. Thus, in addition to anaromatic group, J′ may have fluorine, chlorine, or sulfonate groups.Exemplary diamine reactants of this type include phenylene diamine, afluoromethyl phenylene diamine such as a phenylene diamine in the paraor meta configuration with one to four fluoromethyl groups, each ofwhich may have one to three fluorine atoms, an alkyl fluoromethylphenylene diamine with a mixture of alkyl and fluoromethyl substituents,or a phenylene triamine with no more than one amino group havingsubstituents, may also be used. For example,tetrakis-(2,3,5,6-trifluoromethyl)-1,4-diamino benzene,bis-(2,5-trifluoromethyl)-1,4-diamino benzene, or2-fluoromethyl-bis-(3,5-difluoromethyl)-1,4,-diamino benzene may beused.

J′ may also be a polynuclear aromatic group, such as a naphthalenegroup, an acenaphthene group, an acenaphthylene group, a fluorene group,a phenalene group, or an anthracene group, any of which may besubstituted at any non-amino carbon atom with substituted orunsubstituted alkyl or aryl groups or halogens, or may be partiallysaturated (e.g. dialin, tetralin groups). J′ may also be a substitutedor unsubstituted indene, indane, or indole group.

J′ may also be a phenyl containing group having the general structure offormula (12)

where R⁷ is a substituted or unsubstituted alkyl, aryl, or polyaromaticgroup, any of which may be substituted at any non-amino carbon atom witha substituted or unsubstituted alkyl or aryl group, or a halogen. Thus,R⁷ may be SO₂, C_(x)H_(2x−y)R⁵ _(y), or C₆H_(5−a)R⁵ _(a), with x, y, anda defined as above.

J′ may also have the structure of formula (5) wherein L′ is a divalentlinking group selected from the group consisting of *—SO₂—*, *—N(R′)—*,*—N(H)—*, *—CF₂—*, *—C(CF₃)₂—*, *—R″—*, and combinations thereof,wherein R′ and R″ independently comprise at least 1 carbon. In anembodiment, R′ and R″ are independently selected from the groupconsisting of methyl, ethyl, propyl, isopropyl, phenyl, and combinationsthereof. For example, L′ may be a linear hydrocarbyl group having from 1to 4 carbon atoms. Other L′ groups include methylene (*—CH₂—*),isopropylidenyl (*—C(Me)₂-*), and fluorenylidenyl:

A phenylenedianiline such as p-phenylenedianiline may be used as adiamine reactant. A polyoctatriazacane may have a mixture of linkinggroups of formula (11) and formula (12).

In an embodiment, a POTA is a crosslinked polymer comprising i) aplurality of trivalent octatriazacane groups of formula (10) covalentlylinked to ii) a plurality of divalent bridging groups J′ according tothe descriptions of J′ above. Each starred bond of a givenoctatriazacane group of formula (10) is covalently linked to arespective one of the bridging groups J′. Additionally, each starredbond of a given bridging group J′ is covalently linked to a respectiveone of the octatriazacane groups.

The polyhexahydrotriazine can be bound non-covalently to water and/or asolvent (e.g., by hydrogen bonds).

Exemplary non-limiting divalent bridging groups K′ or J′ include:

and combinations thereof.

In some cases, the divalent bridging group K′ or J′ may be an oligomer,such as a linear or branched polyether, polyester, polystyrenic,polyacrylate, polymethacrylate, polycyclooctene, polyamide, polysulfone,or polynorbornene, or a derivative thereof. Oligomer groups that may beused include:

(polyether), wherein each R is independently hydrogen, alkyl, aryl, oran organic group containing a heteroatom except for nitrogen or sulfur;

(polyester), wherein each R is independently CH₂ or CR′₂, wherein eachR′ is independent H, alkyl, aryl, or an organic group containing aheteroatom except for nitrogen or sulfur;

(polystyrenic), wherein each R is independently hydrogen, alkyl, aryl,or an organic group containing a heteroatom except for nitrogen orsulfur;

(polyacrylate), wherein each R is independently hydrogen, alkyl, aryl,or an organic group containing a heteroatom except for nitrogen orsulfur;

(polymethacrylate), wherein each R is independently hydrogen, alkyl,aryl, or an organic group containing a heteroatom except for nitrogen orsulfur;

(polycyclooctene), wherein each R is independently hydrogen, alkyl,aryl, or an organic group containing a heteroatom except for nitrogen orsulfur;

(polyamide), wherein each R is independently hydrogen, alkyl, aryl, oran organic group containing a heteroatom except for nitrogen or sulfur;

(polysulfone), which may be substituted at any benzene ring;and

(polynorbornene), wherein each R is independently hydrogen, alkyl, aryl,or an organic group containing a heteroatom except for nitrogen orsulfur.

Each bridging group K′ or J′ may be any of the trivalent or divalentbridging groups described above, so a given PHA, PHT, or POTA materialmay have a mixture of divalent bridging groups, a mixture of trivalentbridging groups, or a mixture of divalent and trivalent bridging groups.

Oligomers can be used to influence viscoelastic properties of the gelformed by the PHA/PHT/POTA network. It is believed that, because theoligomers typically have some degree of thermoplasticity at themolecular level, increasing the number of such components in the gelwill tend to increase thixotropic behavior of the gel. As the gel issheared, the large thermoplastic constituents deform and allow thesmaller molecules to separate and flow. More thermoplastic constituentsprovide a dimensional flexibility that allows for local phase separationunder shear, leading to increased viscosity shear coefficient at a giventemperature. The size and nature of the small molecules in the gel willalso affect the viscosity shear coefficient. Larger molecules will tendto separate less easily, leading to directionally lower viscosity shearcoefficient, and vice versa. Branching and Van der Walls behavior in thesmall molecules will also have directional effects. Thus, thixotropicbehavior of the gel may be directionally increased by increasing theamount of thermoplastic components in the gel and by reducing size,branching, and unsaturation of the polymerizable monomers beyond thatneeded for polymerization.

The amount of the first material in the gel may also influenceviscoelastic properties. PHA, PHT, and POTA materials not mixed withother materials and cast as films typically have Young's modulus of 6-14GPa, depending on the composition of the material. Includingthermoplastic components will reduce the hardness of the materialsomewhat, but a thermoplastic modified PHA, PHT, or POTA may still havea Young's modulus of 5-10 GPa. The fraction of first material in the geltherefore strongly influences the modulus of the gel.

Typically the gel will contain a mass fraction of the first materialfrom about 0.01 to about 0.3, such as from about 0.05 to about 0.2, forexample about 0.1. In a typical gel, the molar ratio of oligomericcomponents to non-oligomeric components in the first material is fromabout 0.01 to about 0.3, such as from about 0.05 to about 0.2, forexample about 0.1. The oligomeric components of the first materialtypically have a molecular weight of about 1,000 to about 10,000, andmay have a molecular weight distribution, as indicated by polydispersityindex P₁ of about 1 to about 3, where

$P_{z} = \frac{M_{z + 1}}{M_{z}}$$M_{z} = \frac{\sum{m_{i}^{z}n_{i}}}{\sum{m_{i}^{z - 1}n_{i}}}$where m_(i) is the molecular weight of the ith type of molecule in themixture, and n_(i) is the number of molecules of the ith type in themixture. Polydispersity is typically measured using gel permeationchromatography to generate a molecular weight profile of a mixture, fromwhich any polydispersity index may be determined.

Non-limiting exemplary non-oligomeric monomers comprising two primaryaromatic amine groups that may be used in forming the first materialinclude 4,4′-oxydianiline (ODA), 4,4′-methylenedianiline (MDA),4,4′-(9-fluorenylidene)dianiline (FDA), p-phenylenediamine (PD),1,5-diaminonaphthalene (15DAN), 1,4-diaminonaphthalene (14DAN), andbenzidene, which have the following structures:

As noted above, these materials will directionally reduce viscosityshear index of the gel at a given temperature.

The PHA, PHT, and POTA materials useable for forming the first materialas described herein can further comprise monovalent aromatic groups(referred to herein as diluent groups), which do not participate inchemical crosslinking and therefore can serve to control the crosslinkdensity as well as the physical and mechanical properties of the gel andthe final object. Monovalent diluent groups have a structure accordingto formula (13), formula (14), formula (15), and/or formula (16):

wherein W′ is a monovalent radical selected from the group consisting of*—N(R¹¹)(R¹²), *—OR¹³, —SR¹⁴, wherein R¹¹, R¹², R¹³, and R¹⁴ areindependent monovalent radicals comprising at least 1 carbon. Thestarred bond is linked to a nitrogen of a hemiaminal group or ahexahydrotriazine group.

Non-limiting exemplary diluent groups include:

wherein the starred bond is linked to a nitrogen of a hemiaminal groupor a hexahydrotriazine group. Diluent groups can be used singularly orin combination.

Non-limiting exemplary diluent monomers includeN,N-dimethyl-p-phenylenediamine (DPD), p-methoxyaniline (MOA),p-(methylthio)aniline (MTA), N,N-dimethyl-1,5-diaminonaphthalene(15DMN), N,N-dimethyl-1,4-diaminonaphthalene (14DMN), andN,N-dimethylbenzidene (DMB), which have the following structures:

The diluent monomer can be used in an amount of 0 mole % to about 75mole % based on total moles of monomer and diluent monomer.

The three classes of polymers used to make the first material aregenerally made by mixing one or more primary diamines with aformaldehyde-type reagent in a solvent and heating the resultingmixture. To form a POTA, formic acid is also added to the mixture.

A method of preparing a polyhemiaminal (PHA) comprising divalentbridging groups comprises forming a first mixture comprising i) amonomer comprising two or more primary aromatic amine groups, ii) anoptional diluent monomer comprising one aromatic primary amine group,iii) paraformaldehyde, and iv) a solvent. The first mixture is thenpreferably heated at a temperature of about 20° C. to about 120° C. forabout 1 minute to about 24 hours, thereby forming a second mixturecomprising the PHA. In an embodiment, the monomer comprises two primaryaromatic amine groups, and may be a mixture of oligomeric andnon-oligomeric monomers.

The mole ratio of paraformaldehyde to total moles of primary aromaticamine groups (e.g., diamine monomer plus optional monoamine monomer) ispreferably about 1:1 to about 1.25:1, based on one mole ofparaformaldehyde equal to 30 grams.

A method of preparing a polyhexahydrotriazine (PHT) having divalentbridging groups comprises forming a first mixture comprising i) amonomer comprising two aromatic primary amine groups, ii) an optionaldiluent monomer comprising one aromatic primary amine group, iii)paraformaldehyde, and iv) a solvent, and heating the first mixture at atemperature of at least 150° C., preferably about 165° C. to about 280°C., thereby forming a second mixture comprising a polyhexahydrotriazine.The heating time at any of the above temperatures can be for about 1minute to about 24 hours. A mixture of primary diamine monomers mayinclude oligomeric and non-oligomeric species.

Alternatively, the PHT can be prepared by heating the solutioncomprising the PHA at a temperature of at least 150° C., preferablyabout 165° C. to about 280° C. even more preferably at about 180° C. toabout 220° C., and most preferably at about 200° C. for about 1 minuteto about 24 hours.

A method of preparing a polyoctatriazacane comprising divalent bridginggroups comprises forming a mixture comprising i) a monomer comprisingtwo or more primary aromatic amine groups, ii) an optional diluentmonomer comprising one aromatic primary amine group, iii) an aldehyde,and iv) a solvent. The mixture is stirred while formic acid is added.Any aldehyde may be used, such as formaldehyde, paraformaldehyde,acetaldehyde, benzaldehyde, or the like. The equivalence ratio ofaldehyde to total moles of primary aromatic amine groups (e.g., diaminemonomer plus optional monoamine monomer) is preferably about 1:1 toabout 1.25:1. Formic acid is generally added in sub-stoichiometricquantities, such as less than 0.8 equivalents, between about 0.1equivalents and about 0.5 equivalents, for example about 0.5equivalents. A mixture of primary diamine monomers may includeoligomeric and non-oligomeric species.

Oligomers may be included in a PHA, PHT, or POTA polymer by adding oneor more diamine terminated oligomers to the reaction mixture for formingthe PHA, PHT, or POTA polymer. In the context of the present disclosurethe diamine terminated oligomers may be included in the reaction mixturewith the formaldehyde-type reagent and the polymerizable monomers, andoptionally with formic acid to form a POTA. The process described abovemay be followed to form an interpenetrated network of thermoplasticmodified PHA, PHT, and/or POTA and polymerized polymerizable monomers.

The solvent used for the reaction mixture may include a polymerizablemonomer. The polymerizable monomer is a molecule that may be polymerizedunder controlled conditions, and that does not polymerize substantiallyat conditions used to form PHA, PHT, and POTA materials. Useful reactiveembodiments may polymerize in the presence of a polymerizationinitiator, or by thermal energy, and typically exhibit degree ofpolymerization less than about 20% at temperatures below about 150° C.in the presence of a polymerization initiator. Useful polymerizablemonomers include, but are not limited to, styrenics, acrylates,methacrylates, vinyl esters, unsaturated polyesters, and derivativesthereof. In some cases, the polymerizable monomer, or a mixture ofpolymerizable monomers, may be used as the solvent, with no unreactivesolvent included in the reaction mixture.

Solvents that may be used in the reaction mixture include dipolaraprotic solvents such as, for example, N-methyl-2-pyrrolidone (NMP),dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF),N,N-dimethylacetamide (DMA), propylene carbonate (PC), and propyleneglycol methyl ether acetate (PGMEA).

A PHA film can be made by disposing a mixture comprising apolyhemiaminal and a solvent prepared as described above on a surface ofa substrate to form a structure comprising an initial film layercomprising the polyhemiaminal, solvent and/or water. The initial filmlayer is heated at a temperature of about 20° C. to about 120° C. forabout 1 minute to about 24 hours, thereby forming a structure comprisinga polyhemiaminal (PHA) film layer on the covered surface of thesubstrate. The PHA film layer thus formed is substantially free ofsolvent and/or water. A film layer of this sort may be made in alocalized area using the apparatus of FIGS. 1 and 2 as part of a 3Dprinting process for producing an object. If a polymerizable monomer ofthe type described above is included in the mixture, along with apolymerization initiator, the PHA film layer may be an organogel priorto polymerization of the polymerizable monomer. Subsequent activation ofthe polymerization initiator causes the polymerizable monomer topolymerize and form a film with a network of the polymerizable monomersinterpenetrated with the PHA network.

A PHT film may be made from the PHA film described above, prior tocross-linking any polymerizable monomers, by heating the film layer madeby the process above at a temperature of at least 150° C., preferablyabout 165° C. to about 280° C. even more preferably at about 180° C. toabout 220° C., and most preferably at about 200° C., thereby forming astructure comprising a polyhexahydrotriazine (PHT) film layer disposedon the covered surface of the substrate. The heating time at any of theabove temperatures can be about 1 minute to about 24 hours. Theresulting PHT film layer is substantially free of solvent and water. Thehemiaminal groups of the PHA film are substantially or wholly convertedto hexahydrotriazine groups by heating the PHA film at a temperature inthis range. If a polymerizable monomer is present with an initiator, andthe polymerizable monomer has a reactivity such that polymerization mayoccur at temperatures above about 150° C., heating the PHA filmcontaining the polymerizable monomer to a temperature above about 150°C. will result in converting the PHA to PHT and in polymerization of thepolymerizable monomers to form an interpenetrated network of PHT andpolymerized monomers.

A polyoctatriazacane film may be coated onto a substrate by forming afirst mixture comprising i) a monomer comprising two aromatic primaryamine groups, ii) an optional diluent monomer comprising one aromaticprimary amine group, iii) an aldehyde, and iv) a solvent, coating themixture on the substrate to form a precursor layer, and thendistributing formic acid over the precursor layer to form apolyoctatriazacane coating. The substrate can be any structurally strongsubstrate, such as a semiconductor wafer (e.g., silicon wafer), mostmetals, refractory materials, and other polymers. Any suitable coatingtechnique (e.g., spin coating, dip coating, roll coating, spray coating,and the like) may be used. An adhesive bond may be formed in some casesif the first mixture is allowed to, or able to, penetrate into thesurface of the substrate before reacting with the formic acid. If apolymerizable monomer is included in the first mixture with apolymerization initiator, the polymerization initiator may besubsequently activated, for example by heating, to form a network of thepolymerizable monomer that is interpenetrated with the POTA network.

A material having a mixed PHA/PHT/POTA network interpenetrated with apolymerizable monomer network may be made by separately forming PHA,PHT, and POTA materials, as described above, dissolving the materials inany of the solvents described above, mixing in a polymerizable monomeras described above, with a polymerization initiator, and activating theinitiator to polymerize the polymerizable monomers.

In some cases more than one polymerizable monomer may be included. Anymixture of the polymerizable monomers listed above may be made topolymerize into an interpenetrated network with a PHA, PHT, POTA, ormixture thereof. Additionally, a reaction polymer, such as apolyurethane, polyisocyanurate, melamine resin, or epoxy resin may bemade to interpenetrate with a PHA, PHT, POTA, or mixture thereof bydissolving the PHA, PHT, and/or POTA in a solvent, adding a firstmonomer to the mixture, for example an isocyanate or polyisocyanate inthe case of polyurethane and polyisocyanurate or a phenol in the case ofthe epoxy resin, and then adding a second monomer reactive with thefirst monomer to the mixture, for example polyol for polyurethane andpolyisocyanurate or epoxide for an epoxy resin. An initiator or catalystmay be added as needed to produce the desired interpenetrating polymer.

The materials described above may be used to form an object by forming agel including polymerized PHA, PHT, or POTA, dispensing the gel onto asubstrate, and then hardening the gel by activating the polymerizationinitiator. The gel may be dispensed into a pattern, if desired, prior tohardening by using a dispenser that can form a pattern or by using apatterned substrate. The pattern may be a two dimensional patterncomprising a single layer of gel having a uniform thicknesscharacteristic of a single application of gel to the substrate.Alternately the pattern may be a three dimensional pattern comprisingmultiple layers of gel applied using repeated applications of gel layerover gel layer.

PHA, PHT, and POTA materials are depolymerizable. Depolymerizationmaterials such as strong acids, hot solvents, and in some cases strongor weak bases, optionally photon-assisted with, for example, ultravioletlight, may dismantle such polymers into constituent monomers. Localizedapplication of depolymerization materials may be used to modify surfacesof such materials, which can be useful in repairing or removing unwantedtextures and shapes from the surface. In this way, PHA, PHT, and POTAmaterials may be described as “healable” materials. Such properties ofPHA, PHT, and POTA materials may be equally useful in interpenetratednetworks of PHA, PHT, and POTA materials with polymerizable monomernetworks. The PHA, PHT, or POTA portion may be locally depolymerized byapplying a solvent, such as acetone, along with a light source such as aUV lamp, to dismantle a local portion of the PHA, PHT, and/or POTAnetwork to monomers. The monomers can be mixed with more gel, asdescribed above, or the monomers can be removed and replaced with gel,and the gel can be hardened as described above to repair the article.

Sources of the materials may be coupled to a 3D printing apparatus toform an object by performing a patterned deposition of a curablematerial according to the embodiments described herein. The sources maybe ampoules, tanks, or vessels containing a PHA, PHT, or POTA material,or a mixture thereof, in a solvent or organogel including polymerizablemonomers and initiator. The sources may also be ampoules, tanks, orvessels containing PHA, PHT, or POTA precursors, solvents, polymerizablemonomers, and initiators separately or in non-reactive mixtures.

FIG. 1 is a schematic side view of a 3D printing apparatus 100 accordingto one embodiment. The apparatus 100 comprises a 3D printer 102 and asource 104 of a print medium containing a PHA, PHT, and/or POTA materialdissolved in polymerizable monomers and optionally a solvent. The 3Dprinter 102 includes a stage 106 for a substrate or workpiece 108, and adispenser 110 for dispensing the print material onto the substrate 108.The substrate 108 can be any suitable substrate for receiving a 3Dprinted object. Non-limiting examples of these materials includesemiconductor wafers (e.g., silicon wafers), most metals, refractorymaterials, and other polymers. In some aspects, a substrate may be,without limitation, an electronic device, microchip, microelectronicdevice, printed circuit board, hard disk drive platter, a portion offluid filter, and portion of a hydrocarbon (e.g., petroleum, naturalgas, or petro-chemical) processing facility such as a pipe, pipeline,fluid pumping device, distillation column, a reaction vessel, or storagetank.

The stage 106 may comprise an x-y-z actuator for positioning thesubstrate 108 in three dimensions. The dispenser 110 may be actuated inone, two, or three dimensions. In FIG. 1, the dispenser 110 has a nozzle112 coupled to an articulated positioning arm 114 with a 3-axisrotational positioner 116 coupled to a two-arm translation arm 118,which is in turn coupled to a carriage 120. Such a positioning apparatusmay be used to position the dispensing tip of the nozzle 112 at anylocation in three dimensions and pointing any direction. A source 122 ofconstant pressure, such as a pressurized gas, may be used to force theprint material steadily through the nozzle 112. The source 122 ofconstant pressure is typically coupled by a conduit 124 to a head spaceinside the source 104 of print medium. The source 104 of print medium iscoupled to the 3D printer 102 by a conduit 126 that may be a flexible orrigid tube or pipe. The conduit 126 is shown coupled to the 3D printer102 at the carriage 120 in FIG. 1, but the conduit 126 may be coupled tothe 3D printer at any convenient location from the carriage 120 to thenozzle 112.

FIG. 2 is a schematic side view of a 3D printing apparatus 200 accordingto another embodiment. The apparatus 200 comprises the 3D printer 102and two sources 204A, 204B of precursors for forming a print mediumcontaining a PHA, PHT, and/or POTA material. There are two sources 204A,204B shown in FIG. 2 for illustration, but any number of sources may beused. In an embodiment where two sources 204A and 204B are used, thefirst source 204A may have a first precursor mixture that is unreactive,and the second source 204B may have a second precursor mixture that isunreactive, such that mixing the first and second precursor mixturesforms a gel containing a PHA, PHT, and/or POTA material, a polymerizablemonomer, and a polymerization initiator. In embodiments with three ormore sources, a first source may contain a primary diamine mixture,optionally with a solvent, a second source may contain a mixture offormaldehyde and polymerizable monomers, optionally with a solvent andformic acid if a POTA material is to be included, and a third source maycontain a polymerization initiator, optionally with a solvent.Alternately, each component may be contained in a separate source.

Each source 204A and 204B has a respective source 222A, 222B of constantpressure coupled to a head space of each respective source 204A, 204B bya conduit 222A, 222B. Flow from each source 204A, 204B proceed through arespective conduit 226A, 226B. A mixer 228 may couple the conduits 226A,226B, such that a combined reactive mixture is delivered through theconnection conduit 230 to the 3D printer 102. The mixer 228 andconnection conduit 230 may be temperature controlled to control thedegree of reaction in the connection conduit 230. If no reaction isdesired, the mixer 228 and connection conduit 230 may be cooled byjacketing with a cooling medium. Valves 232A, 232B may be provided tocontrol flow of the first and second precursor mixtures from therespective sources 204A, 204B.

The mixer 228 is shown in FIG. 2 at a location before any precursorsreach the 3D printer 102, but the mixer may be located anywhere betweenthe precursor vessels 204A, 204B and the nozzle 112, for example on thearticulated positioning arm 114.

FIG. 3A is a cross-sectional diagram of a nozzle 300 according to oneembodiment that may be used as the nozzle 110 to dispense a gel onto asubstrate. The nozzle 300 has an inlet 302 and an outlet 304 of a flowpath 306 through the nozzle 300. The flow path 306 has a diameter thatdecreases from the inlet 302 to the outlet 304, but the decreasing flowpath is optional. The flow path may have a constant diameter, a diameterthat increases from the inlet 302 to the outlet 304, or a diameter thatchanges according to any desired pattern. The nozzle 300 has a jacket308 that encloses a flow path 310 for a thermal control medium. Thethermal control medium may flow into the jacket 308 through an inlet312, may flow through the flow path 310, and may flow out of the jacket308 through an outlet 314. The thermal control medium may be used toapply heat to the nozzle 300 to control physical properties such asviscosity of a material being dispensed through the nozzle 300, or toactivate a reaction among components of a material being dispensedthrough the nozzle 300. The nozzle 300 may, for example, be used toperform any of the methods described herein. Alternately, the jacket 308may contain a resistive heating medium with power leads disposed throughthe inlet 312 and the outlet 314. The outside of the nozzle 300 may beinsulated, if desired, to prevent heat loss and unwanted exposure toheated surfaces of the nozzle 300.

FIG. 3B is a cross-sectional view of a nozzle 350 according to anotherembodiment that may be used as the nozzle 110. The nozzle 350 has mostof the features of the nozzle 300, with an additional concentric flowpath. The nozzle 350 has a first inlet 352 and a first outlet 354 thatform a first flow path 366, and a second inlet 356 and a second outlet358 that form a second flow path 368 separated from the first flow path366 by an annular wall 360. The second flow path 366 is annular andsurrounds the first flow path 366. The nozzle 350 may be used to keeptwo streams separate until they leave the nozzle 350 in the event thetwo streams are reactive. The nozzle 350 may thus be used to dispense afirst mixture through the first flow path 366 and a second mixturethrough the second flow path 368 such that the first and second mixturesreact upon leaving the nozzle 350 and form a gel material after leavingthe nozzle 350. It should be noted that the annular second flow path 366is shown in FIG. 3B having a constant cross-sectional flow area, but theannular flow path 366 may have a cross-sectional flow area that changesaccording to any desired pattern.

An object may be made by 3D printing using the apparatus and methodsdescribed herein. A method of forming an object may include flowing afluid containing a PHA, PHT, or POTA precursor, with one or morepolymerizable monomers, and optionally a solvent, to the nozzle of a 3Dprinter, heating the fluid to a temperature of at least about 50° C.,dispensing the fluid in a pattern onto a substrate, and developing thefluid into an interpenetrating network of PHA, PHT, and/or POTA withpolymerized monomers. If the precursor includes polymerizable monomersand polymerization initiators, the precursor may be a gel, which may behardened by treating the object with heat or ultraviolet radiation.Dispensing the precursor in a pattern may include forming a first filmof the precursor according to the film-formation processes describedherein, and forming a second film of the precursor on the first film.

The precursor may be a PHA, PHT, or POTA polymer dissolved in a solventthat includes polymerizable monomers and polymerization initiator, orthe precursor may be a mixture of monomers that form a PHA, PHT, or POTApolymer when reacted together with other polymerizable monomers andpolymerization initiators. A first mixture may contain a primarydiamine, a second mixture may contain a formaldehyde-type reagent,polymerizable monomers, and, optionally, formic acid for forming anobject containing POTA, and a third mixture may contain polymerizationinitiators. Each of the first, second, and third mixtures may be flowedthrough a separate pathway to prevent premature reaction of thecomponents. The first and second mixture may be mixed together at adesired time to start the reaction. For example, using the apparatus200, the first and second mixtures may be mixed at the mixer 228.

Heating the precursor to a temperature of at least about 50° C. may beaccomplished by supplying heat to the nozzle of the 3D printer. Forexample, either the nozzle of FIG. 3A or the nozzle of FIG. 3B may beused with the apparatus 100 or the apparatus 200 to provide heat. Theprecursor may be heated to at least 50° C. in the nozzle, dispensed ontothe substrate in a pattern to form a precursor object, and the precursorobject may be cured at a temperature of at least about 120° C. to hardenthe object. Alternately, the precursor may be heated to at least 120° C.in the nozzle, dispensed onto the substrate in a pattern to form aprecursor object, and the precursor object may be cured at a temperatureof about 200° C. to harden the object.

It should be noted that an object may include more than one type of PHA,more than one type of PHT, or more than one type of POTA by changing themonomers used to form the polymer during formation of the object. Anobject may also include PHA and PHT, PHA, and POTA, PHT and POTA, orPHA, PHT, and POTA in any desired mixture by changing the monomers usedto form the polymer. Thus, an object may be formed that is a mixture ofPHA, PHT, and/or POTA to provide different parts of the object withdifferent physical properties.

FIG. 4A is a process diagram illustrating aspects of the processesdescribed herein. In FIG. 4A, a gel material 400 is deposited on asubstrate 402 using a nozzle 403, which may be the nozzle 110, thenozzle 300, or the nozzle 350 in any of the apparatus 100 or 200described above. A simulated micrograph 404 illustrates themicrostructure of the gel material 400. The gel material 400 depicted inthe simulated micrograph 404 contains strands of PHA polymer 406 joinedat hemiaminal centers 407 in a medium containing polymerizable monomers408 and polymerization initiators 410. The components of the gelmaterial 400 may be any of those described herein.

FIG. 4B is a process diagram illustrating other aspects of the processesdescribed herein. In FIG. 4B, the gel material 400 (FIG. 4A) isdeposited in a pattern on the substrate 402. The gel material is exposedto ultraviolet radiation 412 from UV source 414. A simulated micrograph416 illustrates that the radiation transforms the gel material into ahard solid 420 by activating the polymerization initiators 410 (FIG. 4A)and linking up the polymerizable monomers 408 (FIG. 4A) into polymerchains 418 interpenetrating with the PHA polymer strands 406.

FIG. 4C is a process diagram illustrating other aspects of the processesdescribed herein. In FIG. 4C, a gel medium 424 is disposed in a frame422 with a plurality of fibers 426 immersed in the gel medium 424. Thesimulated micrograph 404 shows the gel structure, with a fiber 426.

FIG. 4D is a process diagram illustrating other aspects of the processesdescribed herein. In FIG. 4D, the gel medium 424 (FIG. 4C) is exposed toultraviolet radiation 412 from UV source 414, transforming the gelmedium to a hard solid 428 that is reinforced by the fibers 426. Asimulated micrograph 430 illustrates that the radiation transforms thegel material into the hard solid 428 by activating the polymerizationinitiators 410 (FIG. 4C) and linking up the polymerizable monomers 408(FIG. 4C) into polymer chains 418 interpenetrating with the PHA polymerstrands 406 and the fibers 426. In this way, a percolating network maybe formed.

Example Formation of PHA Films:

4,4′-Oxydianiline (ODA, 0.400 g, 2.0 mmol) and paraformaldehyde (PF,0.300 g, 10.0 mmol, 5 eq.) were weighed into a 2-Dram vial with equippedwith a stirbar. NMP (6 mL, 0.33 M with respect to ODA) was added to thevial under nitrogen. The vial was capped but not sealed. The solutionwas stirred at 50° C. for 30 minutes (time sufficient to form solubleoligomers in NMP). The clear and colorless solution was then filteredthrough a nylon syringe filter (0.45 micrometers) onto a glass platewith aluminum tape (80 micrometers thickness) boundaries. The film wascured at 50° C. for 24 hours. The clear and colorless polyhemiaminalfilm was then carefully peeled from the glass plate using a razor blade.The process was repeated with an ODA:PF mole ratio of 1:6.7, and againwith an ODA:PF mole ratio of 1:10. PHA films were also preparedaccording to the same process, but substituting 4,4′-methylenedianiline(MDA) for ODA at an MDA:PF mole ratio of 1:5, substituting4,4′-fluorenylidenedianiline (FDA) for ODA at an FDA:PF mole ratio of1:5, and substituting poly(ethylene glycol) diamine (PEG-DA) for ODA ata PEG-DA:PF mole ratio of 1:5.

Example Formation of PHA Organogels with Polymerizable Monomer:

PEG diamine (8 kDa diamine, 0.230 g) and paraformaldehyde (PF, 0.0038 g,4.4 equiv.) were weighed into a 2-Dram vial equipped with a stirbar.Styrene (2.3 mL) was added to the vial under nitrogen. The vial wascapped but not sealed. The solution was stirred at 50° C. for 1.5 hoursuntil gelation. After leaving under ambient light for 48 hours, the gelchanged in appearance from a flexible, elastic gel to a hardenedtranslucent plastic, consistent with polystyrene.

Example Formation of PHT Films:

ODA (0.400 g, 2.0 mmol) and PF (0.150 g, 5.0 mmol, 2.5 equiv) wereweighed into a 2-Dram vial equipped with a stirbar. NMP (6 mL, 0.33 Mwith respect to ODA) was added to the vial under nitrogen and the vialwas capped. The vial was not sealed. The solution was allowed to stir at50° C. for 30 minutes (time sufficient for solubility of reagents inNMP). The clear and colorless solution was then filtered through a nylonsyringe filter (0.45 micrometer) onto a leveled glass plate withaluminum tape (80 micrometers thickness) boundaries and allowed to cureaccording to the following ramping procedure: 22° C. to 50° C. over 1hour; then 50° C. to 200° C. over 1 hour, and hold at 200° C. for 1hour. The yellow film was then carefully peeled from the glass plateusing a razor blade. The process was repeated with an ODA:PF mole ratioof 1:5, and again with an ODA:PF mole ratio of 1:10. PHA films were alsoprepared according to the same process, but substituting4,4′-methylenedianiline (MDA) for ODA at an MDA:PF mole ratio of 1:2.5,and substituting 4,4′-fluorenylidenedianiline (FDA) for ODA at an FDA:PFmole ratio of 1:2.5. Such films may be used in 3D printing processes toform an object by repeatedly depositing PHT films on a substrate.

Example Formation of POTA Material:

In one example, 0.050 g of p-phenylenedianiline (0.462 mmol, 1.0equivalents, purchased from Sigma-Aldrich Co., LLC, of St. Louis, Mo.and stored under nitrogen) and 0.0277 g paraformaldehyde (0.924 mmol,2.0 equivalents, washed with water, acetone, the diethyl ether, thendried over P2O5 prior to use) were combined in a dried vial with stirbarin a nitrogen-filled glovebox with 0.5 mL of dry DMSO (refluxed overCaH2 for 96 hours prior and then distilled prior to use). Formic acid,0.004 g, was then added by syringe to the solution (0.231 mmol, 0.5equivalents). The result was an orange solution ofpoly-N,N,N-(p-phenylenedianiline)-octatriazacane.

The foregoing exemplary films and materials may be used as part of aninterpenetrating network of PHA, PHT, and/or POTA with polymerizablemonomers by including polymerizable monomers, along with apolymerization initiator, in the reaction mixture. The PHA, PHT, and/orPOTA network may be developed as described above to form a gel, and thenthe gel can be hardened by activating the polymerization initiator.Heating the gel, or exposing the gel to ultraviolet light, activates thepolymerization initiator and polymerizes the polymerizable monomers.

The materials described herein may be fiber impregnated by immersing afiber filler in the reaction mixture before gelling and hardening. Thefiber filler may be a mat or an unstructured fiber mass. Polymerizingthe reaction medium according to the two-step process described hereinresults in a fiber-reinforced solid polymer percolating network of PHA,PHT, and/or POTA with interpenetrating polymer network and fibers. Thefibers described above may be carbon fibers, carbon nanotubes,fiberglass, metal fibers, cloth fibers such as silk and cotton threads,which may be formed into a fabric.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

We claim:
 1. A composition, comprising: an interpenetrating network of afirst material comprising a polyhemiaminal (PHA), polyhexahydrotriazine(PHT), polyoctatriazacane (POTA), or combination thereof; an oligomerselected from the group consisting of polyether, polyester,polystyrenic, polyacrylate, polymethacrylate, polycyclooctene,polyamide, polynorbornene, and derivatives thereof; and a divalentbridging group of formula (5):

wherein L′ is a divalent linking group selected from the groupconsisting of *—O—*, *—S—*, *—N(R′)—*, *—N(H)—*, *—R″—*, andcombinations thereof, wherein R′ and R″ independently comprise at least1 carbon; and a second material comprising a cured polymer selected fromthe group consisting of a styrenic polymer, an acrylate polymer, amethacrylate polymer, a vinyl ester polymer, an unsaturated polyesterpolymer, and derivatives thereof.
 2. The composition of claim 1, furthercomprising a filler.
 3. The composition of claim 2, wherein the filleris a fiber material.
 4. The composition of claim 1, further comprising afiber filler, wherein the composition is a percolation network.